<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .header{
            height: 100px;
            background-color: green;
        }
        .container{
            
        }
        .footer{
            clear: both;
            height: 100px;
            background-color: gray;
        }
    </style>
</head>
<body>
    <div id="header">header</div>
    <div id="container" class="column">
        <div id="center">
            <p>占位文字</p>
            <p>占位文字</p>
            <p>占位文字</p>
            <p>占位文字</p>
        </div>
    </div>
    <div id="left" class="column">
        <p>占位文字</p>
        <p>占位文字</p>
        <p>占位文字</p>
        <p>占位文字</p>
    </div>
    <div id="right" class="column">
        <p>占位文字</p>
        <p>占位文字</p>
        <p>占位文字</p>
        <p>占位文字</p>
    </div>
    <div id="footer">footer</div>
</body>
</html>